bind camera to marker via python
You can do this quite simply without the bpy.ops.  For testing I made a py dict from some of your xml data.

import bpy
context = bpy.context
scene = context.scene
markers = {
            "F_00": {"frame":0, "camera":"Camera.003", "frame_time":0.04},
            "F_335": {"frame":335, "camera":"Camera.005", "frame_time":13.92},
           }
for name, m_data in markers.items():
    # add a marker 
    marker = scene.timeline_markers.new(name, frame=m_data["frame"])
    marker.camera = scene.objects.get(m_data["camera"])